BIOSYNTHESIS OF POLY(3-HYDROXYBUTYRATE-CO-3-HYDROXYVALERATE) IN RHODOCOCCUS RUBER

The biosynithesis of the 3-hydroxyvalerate (3HV) monomer of the polyhy droxyalkanoate produced from glucose by Rhodococcus ruber was investig ated using nuclear magnetic resonance analysis. Spectra obtained for p olymer produced from [6-C-13]-, [2-C-13]-, and [1-C-13]glucose were co mpatible with carboxylation of pyruvate followed by TCA cycle reaction s to yield succinate, which is a precursor of propionyl-CoA in the bio synthesis of 3HV in this organism. Carboxylation of pyruvate may occur directly or involve methylmalonyl-CoA transcarboxylase but the latter process is more probable as it provides a route for recycling oxaloac etate, which is essential for the pathway to operate, The observed inc orporation of label from (NaHCO3)-C-13 into C-3 of 3HV monomers cannot occur via forward reactions of the TCA cycle but may be explained by direct carboxylation of pyruvate, followed by reverse reactions of the TCA cycle to yield succinyl-CoA. This minor route accounts for at lea st 12% of the carbon flux in the synthesis of 3HV monomer units. Inhib itors of key enzymes of possible pathways for polyhydroxyalkanoate bio synthesis in R. ruber were tested. Addition of monofluoroacetate, an i nhibitor of aconitase, to cultures decreased production of 3HV, suppor ting the proposed major route for 3HV synthesis.